Switch contact arrangement with an erosion display for the switch contacts

ABSTRACT

The invention relates to a switch contact arrangement with a first moving switch contact, with a second switch contact, provided for the first switch contact and with an erosion display, for the switch contacts. The erosion display comprises an erosion pointer and a display surface or display edge. The display pointer follows the movement of the first switch contact and, on closing the contacts, then only extends over the display surface or display edge when the value for the erosion of the switch contacts is less than a given maximum value. In order to be able to shorten the display pointer in the unused condition without a special tool to give a separation from the display surface or display edge, the value of which corresponds to the value of the maximum permitted erosion of the switch contacts, at least one marking for the cutting of the display pointer is provided, whereby the marking is separated from the display surface or display edge by the maximum permitted erosion of the switch contacts.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/DE2003/002591, filed Jul. 30, 2003 and claims the benefitthereof. The International Application claims the benefits of GermanPatent application No. 10243835.8 DE filed Sep. 13, 2002, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention is in the area of electrical switches provided with aswitch contact arrangement fitted with a first moving switch contact,and a second switch contact provided for the first switch contact, andis intended for use in the design and construction of an erosion displayfor the said switch contacts.

BACKGROUND OF THE INVENTION

In an older design of a switch contact arrangement known from documentDE 17 64 678 U, an erosion display is provided in which an erosionpointer held against a moving contact by spring pressure is free to movein a guide. The end extending beyond the guide represents a measure ofthe contact erosion. Additionally a metal sheet can be fitted andprovided with indicator markings against which the extent of the erosioncan be read off. The metal sheet is fastened to the switch housing bymeans of an elongated hole and screws to position it precisely at apoint of origin. This positioning must be carried out with the switchhousing open by making fine adjustments to the sheet metal indicator,which adds up to a considerable amount of work if there is a number ofcircuit-breakers in a switch installation.

In a further known switch contact arrangement for a low-voltagecircuit-breaker, the erosion display comprises an erosion pointer and adisplay surface or display edge. The erosion pointer follows themovement of the first switch contact and, with the contacts closed, thenextends beyond the display surface or display edge only when the valuefor the erosion of the switch contacts is less than a given maximumvalue (Instruction Manual for Circuit-Breaker 3WN6, Siemens AG, Germany,1998). In this known switch contact arrangement, the moving switchcontact has a contact holder and a plurality of contact levers supportedon the contact holder by means of contact force springs. The metalerosion pointer is supported on one of the contact levers and located ina hole drilled in the contact holder in the direction of force of thecontact force spring. A recess in the contact holder serves as aninspection hole, one side of which opens to the drill hole, such thatthe end of the erosion pointer facing away from the contact lever onlyextends into the inspection aperture when there is a permitted amount oferosion on contact surfaces formed on the contact levers(contactmembers). If the value for the erosion on these contact surfaces isgreater than the predefined maximum value, the erosion pointer no longerextends into this inspection hole. This then indicates that the switchcontact arrangement needs to be renewed. When the worn switch contactshave been replaced with new switch contacts, a new erosion pointer mustbe inserted into the drill hole on the contact holder and must then beshortened with the contacts closed so that after shortening, its endpointing away from the contact lever extends into the inspection hole bythe value predefined for the maximum erosion, for example 2.7 mm. Thisshortening requires a special tool which can be inserted into the verynarrow inspection hole. Since fitters regularly exchange worn switchcontact arrangements on the premises of operators of such electricalswitches, the fitters must be in possession of this special tool.

Based on a switch contact arrangement with features according to thepreamble of the claims (Instruction Manual for Circuit-Breaker 3WN6,Siemens AG, Germany, 1998) the object of the invention is to design theerosion display in a way that makes shortening the erosion pointereasier.

SUMMARY OF THE INVENTION

This object is inventively achieved in that at least one marking isprovided for cutting the erosion pointer, whereby the marking isseparated from the display surface or display edge by the maximumpermitted erosion of the switch contacts.

By virtue of such a design, a new erosion pointer can be cut short atthe marking by using ordinary, simple tools such as a slottedscrewdriver. The on-site fitter therefore does not need an expensivespecial tool in order to shorten the erosion pointer with the switchcontacts closed, at a point that is separated from the display surfaceor display edge by the maximum value predefined for the erosion.

According to the invention, the term erosion pointer means that elementwhich is clearly visible when it extends beyond the display surface ordisplay edge and which can be shortened without great technical effort,for instance by cutting. Such an element can have any kind ofcross-section, such as polygonal, oval or round, and may also take theform of a stiff strip or tape. This element may be supported on themoving switch contact, directly or via a connecting link, or may befastened to the moving switch contact, or designed as an integralcomponent of the moving switch contact.

In a preferred embodiment of the innovative switch contact arrangementit is envisaged that the marking, in particular that for guiding thecutting edge of a tool, will take the form of a cutting surface orcutting edge. Using such a design the erosion pointer can be shortenedaccurately on the cutting edge or cutting surface without the need forany additional mark on the erosion pointer itself.

So that it will be easier to shorten the erosion pointer, it isenvisaged that the erosion pointer will be made of plastic.

To provide support for the erosion pointer during cutting, and as asimple means of avoiding damage to the erosion pointer duringshortening, a supporting surface can be provided running parallel to theerosion pointer.

In particular the low-voltage circuit-breaker known from theaforementioned instruction manual can also be provided with theinnovative switch contact arrangement because the marking is formed by afirst side of a second recess which is open to the first recess. In thiscase the supporting surface can be formed from a section of the drillhole open to the floor of the first recess. The second recess can formlateral guide surfaces for the tool used for cutting.

In an innovative switch contact arrangement built into an electricalswitch, the erosion pointer can easily be adapted to the dimensionaltolerances of the innovative switch contact arrangement by cutting thepointer as necessary. For this purpose an erosion pointer that extendsbeyond the marking when the switch contacts are closed merely has to beprovided for the innovative switch contact arrangement and then cut offat the marking. An ordinary tool such as a slotted screwdriver can beused for cutting;

BRIEF DESCRIPTION OF THE DRAWINGS

A typical embodiment of a switch contact arrangement for an electricalswitch in the form of a low-voltage circuit-breaker with the innovativeerosion display is shown in FIGS. 1 to 7. These are as follows:

FIG. 1 is a diagram of a low-voltage circuit-breaker with a switchcontact arrangement comprising an erosion display for switch contactsprovided with contact surfaces,

FIG. 2 shows the switch contact arrangement according to FIG. 1 as itfirst appears in its unused condition before the erosion pointer hasbeen shortened,

FIG. 3 shows the switch contact arrangement in its unused condition whenthe erosion pointer is being cut,

FIG. 4 shows the switch contact arrangement in the condition of maximumpermitted erosion of the contact surfaces on the switch contacts,

FIG. 5 is a sectional view of a first section of the switch contactarrangement along the line A—A in FIG. 3

and

FIGS. 6 and 7 are a top view of a second section of the switch contactarrangement with the erosion pointer still not shortened as in FIG. 2,and with the erosion pointer cut as in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The low-voltage circuit-breaker according to FIG. 1 has a housing 1containing a switch contact arrangement (consisting of a moving switchcontact 2 and a static contact 3), an arc quenching chamber 4 and adrive mechanism 6. The said drive mechanism 6 is used in this case toactivate the moving switch contact 2, which has a plurality of contactlevers 8 supported in a pivoting contact holder 7 and arranged parallelto each other (only one contact lever is visible in the figure). Thecontact levers 8 are pivotally attached in a known way to the contactholder 7 by a joint bolt and pre-tensioned by two contact force springs9 each. Flexible conductors 10 serve to connect the contact levers 8 toa lower connecting bar 11. The static switch contact 3 associated withthe moving switch contact 2 is connected to an upper connecting bar 12.The switch contacts 2, 3 are provided with contact surfaces 13, 14(contact members) in the form of superimposed bodies made from a veryspecial material, and consisting of sintered materials containing Ni, Wand other special metals. Since these are comparatively expensive theyare applied in relatively thin layers. The contact surfaces 13, 14 arestill quite thick when the switch contact arrangement is in its unusedcondition, and its material is eroded by an electric arc. It is thusnecessary to ensure that the contact surfaces are melted away fully.Therefore a certain value is specified as the maximum permitted erosionvalue, and the switch contact arrangement includes a display device 15to display the current erosion value. When a new switch contactarrangement is fitted on the electrical switch operator's premises it isdesirable that the erosion display can be set to the value specified forthe maximum permitted erosion without a special tool.

For this purpose the erosion display according to FIG. 2 has a plasticerosion pointer 16, together with a display surface 17 or display edge18 aligned at a first level, the erosion pointer 16 needing to beshortened, with the switch contacts 2, 3 closed, at a marking of theswitch contact arrangement, said marking being in the form of a cuttingsurface 19. This cutting surface 19 is separated from the displaysurface 17 by a distance 20, the value of which corresponds to thespecified maximum erosion value.

The newly inserted erosion pointer is supported on one of the contactlevers 8. For this purpose the said pointer has a collar 21 at its endpointing toward the contact lever. This collar 21 fits into a pocket 22in the contact lever. Between the collar and the far end 23 of a socket24 for one of the contact force springs 9, the contact force spring 9through which the erosion pointer 16 extends is pre-tensioned, holdingthe erosion pointer against the contact lever 8 in such a way that thepointer follows the movement of the contact lever. The far end 23 of thesocket 24 for the contact force spring is the starting point of a drillhole 25 which extends through the contact holder 7 and is open both to afirst side of a first recess 27 forming the display surface 17 and tothe floor 35 of the first recess 27. This drill hole 25 serves as aguide for the erosion pointer 16. The value for the width of the firstrecess 27 in the direction in which the erosion pointer 16 moves is thesame as the value of the distance 20, being the maximum permittederosion value. On the side 28 which points away from the contact holderthe drill hole is open to a first side of a second recess 30 which isalso accessible from above. With the switch contacts 2, 3 closed, a newerosion pointer 16 extends beyond the first side of the second recess 30used as the cutting surface 19 (cf. also FIG. 6).

According to FIG. 3, a slotted screwdriver 31 with its tapered endacting as a cutting edge 32 is pushed sharply downward onto the cuttingsurface 19 in order to cut the erosion pointer 16. For this purpose theside surfaces 33, 34 (cf. FIG. 6) of the second recess 30 act as guidesurfaces for the screwdriver 31.

According to FIG. 5 a section of the drill hole open to the floor 35 ofthe first recess 27 forms a supporting surface 36 for the erosionpointer 16 during cutting. The floor 37 of the second recess is somewhatdeeper, so that a part 38 (cf. FIGS. 3 and 6) of the erosion pointer 16projecting beyond the cutting surface 19 can be cut completely. Othertools may also be used to remove the said part 38 by cutting, filing orsome other means.

According to FIGS. 3 and 7, the end of the erosion pointer 16 is levelwith the cutting surface 19 after cutting, so that when the switchcontact arrangement is in its unused condition said pointer exactlyindicates the maximum permitted erosion value when viewed in relation tothe display surface 17.

According to FIG. 4, the end of the erosion pointer 16 is level with thedisplay surface 17 and can therefore no longer be seen by an observerfrom above when the contact surfaces 13, 14 of the switch contacts 2, 3have been burned away by the predefined maximum permitted value and theswitch contact arrangement needs to be renewed.

1. A switch contact arrangement, comprising: a first moving switchcontact; a second switch contact, provided for the first switch contact;an erosion display for the switch contacts, comprising: an erosionpointer; and a display surface or display edge, wherein the erosionpointer follows the movement of the first switch contact and, with thecontacts closed, extends beyond the display surface or display edge onlywhen the value for the erosion of the switch contacts is less than agiven maximum value; and a marking in the form of a cutting surface orcutting edge and is suitable for guiding the cutting edge of a tool andis provided for cutting the erosion pointer, whereby the marking isseparated from the display surface or display edge by the maximumpermitted erosion of the switch contacts.
 2. The switch contactarrangement according to claim 1, wherein the erosion pointer is madefrom plastic.
 3. The switch contact arrangement according to claim 1,wherein a supporting surface parallel to the erosion pointer is providedin order to support the erosion pointer during cutting.
 4. The switchcontact arrangement according to claim 1, wherein the moving switchcontact has a contact holder and a contact lever supported on thecontact holder by a contact force spring and the erosion pointer of theerosion display is free to slide in a drill hole that acts as a guide inthe contact holder, such that the display surface or display edge isformed by a first side, open to the drill hole, of a first recess in thecontact holder, and the marking is formed by a first side of a secondrecess which is open to the first recess.
 5. The switch contactarrangement according to claim 4, wherein the supporting surface isformed by a section of the drill hole, and said section being open tothe floor of the first recess.
 6. The switch contact arrangementaccording to claim 4, wherein the second recess forms lateral guidesurfaces for the tool.
 7. A method for cutting an erosion pointer in aswitch contact arrangement, comprising: providing an erosion pointerthat extends beyond a marking when a first and second switch contactsare closed; and cutting the erosion pointer at the marking.
 8. Themethod for cutting an erosion pointer according to claim 7, wherein aslotted screwdriver is used as a tool for cutting.